Lithium secondary batteries have high voltage and high capacity compared to conventional nickel cadmium secondary batteries and the like. Specifically, when lithium transition metal composite oxides, such as LiCoO2, LiNiO2 and LiMn2O4 are used as the cathode active material, and carbonaceous materials, such as graphite, carbon fiber and the like are used as the anode active material, high voltage and high capacity of 4V or greater can be achieved. Because lithium secondary batteries have few adverse effects such as short circuits, they have been widely used as power sources for mobile electronic devices such as cell phones, notebook computers, digital cameras and the like.
However, mobile devices are rapidly becoming lighter and smaller, and are being used for a variety of functions. Since mobile devices can be used in both low and high temperatures, higher electric capacities, higher charge/discharge characteristics and greater stability are needed. Conventional lithium batteries using LiCoO2 powder as cathode active materials do not exhibit these battery characteristics. Accordingly, various alternatives have been presented to achieve these characteristics.
For example, methods for coating cathode active materials have been proposed. However, complex processes make these methods difficult to apply.
Methods for improving the packing densities of the active material particles have also been proposed. However, improvements in the desired battery characteristics, such as high voltage stability, thermal stability and high rate discharge characteristics, are limited.
Accordingly, a need exists for composite cathode active materials capable of improving high voltage stability, thermal stability and high rate discharge characteristics of lithium batteries.